Field of the Invention
The ventilated disc according to the present invention is used in the state where the ventilated disc has been incorporated in a disc brake for braking a vehicle.
Disc brakes are hitherto used broadly as braking apparatus for braking vehicles. FIG. 7 shows a disc brake presented in JIS D 0107. A piston 4 is fluid-tightly fitted into a cylinder 3 provided in a cylinder body 2 supported on a stationary portion astride a disc 1 in which the disc 1 which rotates together with a wheel is supported. At the time of braking, pressure fluid is supplied into the cylinder 3 so that a pair of pads 5 and 5 provided on opposite sides of the disc 1 are pressed against the opposite sides of the disc 1.
Other than such a solid disc 6 as shown in FIG. 8, a ventilated disc 7 shown in FIG. 9 is hitherto used as the disc 1 forming such a disc brake. The ventilated disc 7 has a ring-like inner disc portion 8, a ring-like outer disc portion 9, and a large number of connecting ribs (radiator fins) 10. The inner and outer disc portions 8 and 9 are disposed parallelly and coaxially at a distance from each other. The connecting ribs 10 connect respective surfaces of the disc portions 8 and 9 facing each other. Each air channel 11 radially extending is formed between the circumferentially adjacent connecting ribs 10. Such a ventilated disc 7 is fixedly attached to a hub unit which supports the wheel rotatably on the stationary portion, by an attachment portion 12 provided coaxially with the disc portions 8 and 9. When the vehicle is running, the ventilated disc 7 rotates together with the wheel and the air flows in the respective air channels 11 from the inner diameter side to the outer diameter side by centrifugal force to thereby cool the ventilated disc 7.
Such a ventilated disc 7 is employed chiefly in a high-performance vehicle, or the like, which needs great braking ability. Generally, in the conventional ventilated disc 7, as shown in FIG. 10, a plurality of connecting ribs 10 are arranged radially. However, as shown in FIG. 11, a ventilated disc in which connecting ribs 10a are inclined in the direction of rotation of the ventilated disc is also known conventionally.
Further, as shown in FIG. 12, a ventilated disc in which connecting ribs 10b each bent like an arc are inclined in the direction of rotation is also known conventionally, for example, as disclosed in JP-A-8-164828 and JP-B-54-14710. In the ventilated disc in which the connecting ribs 10a or 10b are inclined in the direction of rotation as described above, the pumping effect due to rotation becomes large. Accordingly, when a large amount of heat is generated in braking at the time of high-speed running, a large amount of air is made flow in the air channels 11a or 11b between circumferentially adjacent ones of the connecting ribs 10a or 10b. As a result, the effect of restraining the temperature rising of the ventilated disc is remarkable. In the case of using the ventilated disc shown in FIG. 11 or 12, however, it is necessary to regulate the direction of rotation of the ventilated disc (the counterclockwise direction in FIG. 11 or 12) in order to circulate a large amount of air into the air channels 11a or 11b. It is therefore impossible to standardize parts of the ventilated disc between right and left sides of the vehicle.
In the case of such a ventilated disc 7, as shown in FIGS. 9 to 12, which is generally conventionally used, vibration called judder is apt to be generated at the time of sudden braking or the like in the state of running at a high speed. That is, in each of the conventional structures shown in FIGS. 9 to 12, the distance between circumferentially adjacent ones of the connecting ribs 10, 10a or 10b is narrower on the inner diameter side of the ventilated disc 7 but wider on the outer diameter side thereof. On the other hand, the rigidity of the ventilated disc 7 in its axial direction is larger in portions corresponding to the connecting ribs 10, 10a or 10b, but smaller in portions corresponding to the air channels 11, 11a or 11b. Therefore, a difference between the rigidity in the portions corresponding to the connecting ribs 10, 10a or 10b and the rigidity in the portions corresponding to the air channels 11, 11a or 11b becomes more conspicuous on the outer diameter side than on the inner diameter side. As a result, slight circumferential irregularities are apt to be formed on the opposite surfaces of the ventilated disc 7 in finishing on the opposite surfaces for flattening.
In addition, such circumferential irregularities are also produced by the temperature rising of the ventilated disc 7 at the time of braking. That is, at the time of braking, the pair of pads 5 (FIG. 7) press the ventilated disc 7 from the axially opposite sides of the disc 7 strongly. Then, the temperature of the ventilated disc 7 rises due to the friction between the opposite surfaces of the ventilated disc 7 and the respective pads 5, so that the ventilated disc 7 expands thermally. Such thermal expansion due to the temperature rising becomes more conspicuous in the portions of the connecting ribs 10, 10a or 10b having large thermal capacity than in the portions of the air channels 11, 11a or 11b having small thermal capacity. Thus, the portions corresponding to the connecting ribs 10, 10a or 10b become recess portions, and the portions corresponding to the air channels 11, 11a or 11b become protrusion portions, so that slight irregularities are produced circumferentially. Particularly when the distance between circumferentially adjacent ones of the connecting ribs 10, 10a or 10b on the inner diameter side differs largely from that on the outer diameter side as in the conventional structures shown in FIGS. 10 to 12, the aforementioned irregularities produced by the difference in temperature rising are apt to be large and uneven between the inner diameter side and outer diameter side. Thus, vibration is apt to be produced as mentioned above.
In addition, in the case of the conventional structures shown in FIGS. 10 to 12, it is difficult to make the saving of weight compatible with the enhancement of heat radiation performance. That is, in order to enhance the heat radiation performance, it is considered that the number of the connecting ribs 10, 10a or 10b is increased so that the heat exchange area with the air flowing into the air channels 11, 11a or 11b is enlarged. If the number of the connecting ribs 10, 10a or 10b is increased, however, the weight of the ventilated disc 7 increases correspondingly. Undesirably, the ventilated disc 7 fixed to the wheel has a so-called unsprung load so that even a slight increase in weight results in deterioration in the performance of the vehicle mainly on comfortability. On the other hand, from the point of ensuring the strength of the ventilated disc 7, it is difficult to reduce the thickness of the connecting ribs 10, 10a or 10b so as to restrain the increase in weight.
Taking the foregoing circumstances into consideration, the present invention was developed to realize a ventilated disc which can prevent its axially opposite surfaces from being deformed to undulate circumferentially, and which is light in weight.
Like the aforementioned ventilated disc which has been conventionally known, a ventilated disc according to the present invention comprises a ring-like inner disc portion and a ring-like outer disc portion which are disposed parallelly and coaxially at a distance from each other; and a large number of connecting ribs for connecting opposite surfaces, of the disc portions, facing each other. The ventilated disc rotates together with a wheel while being fixed thereto. Then, the ventilated disc is rubbed by pads supported by the vehicle body at the time of braking.
Particularly, in the ventilated disc according to the present invention, the connecting ribs include a large number of first to fourth connecting ribs. Of those ribs, the first connecting ribs are provided in the inner-diameter-side portions on each of the opposite disc portions, and are long in the radial direction of the opposite disc portions respectively. The second and third connecting ribs are provided alternately circumferentially in the outer-diameter-side portions on each of the opposite disc portions, and are inclined reversely to each other with respect to the radial direction of the opposite disc portions, i.e. symmetric with respect to the radial direction. Each of the fourth connecting ribs is provided at a circumferential center of a portion where a distance between the second and third connecting ribs is largest.
Preferably, the second and third connecting ribs are provided so that a circumferential phase of inner-diameter-side end portions of the second and third connecting ribs coincides with that of the first connecting ribs, and a large number of fifth connecting ribs are provided between radially intermediate portions of the opposite disc portions so that a circumferential phase of the fifth connecting ribs is shifted by half a pitch from that of the first connecting ribs.
Further preferably, a distance between inner-diameter-side end portions of circumferentially adjacent ones of the first connecting ribs, a distance which is between outer-diameter end portions of circumferentially adjacent ones of the second and third connecting ribs and which is the narrowest one, a distance between outer-diameter-side end portions of circumferentially adjacent ones of the second and fourth connecting ribs, and a distance between outer-diameter-side end portions of circumferentially adjacent ones of the third and fourth connecting ribs are made substantially equal to one another.
In the case of such a ventilated disc according to the present invention as configured thus, a large difference in distance can be prevented from appearing between circumferentially adjacent ones of the connecting ribs. Accordingly, the opposite surfaces of the ventilated disc can be prevented from being deformed to undulate circumferentially with the finishing process applied to the opposite surfaces or the temperature rising at the time of braking. In addition, the first to fifth connecting ribs which are respectively shorter than connecting ribs constituting conventional structures are disposed radially and circumferentially. Accordingly, the total surface area of the connecting ribs can be enlarged without reducing the strength or without increasing the weight. It is therefore possible to realize a ventilated disc which is light in weight. Further, because the second and third connecting ribs are provided to be inclined reversely to each other, it is possible to realize a ventilated disc which can circulate a large amount of air inside the ventilated disc so as to exhibit an excellent cooling effect and in which the direction of attachment is not limited.